Extraneous pickup caused by undesirable electro-magnetic, mechanical or thermal disturbances is often recorded as data in many electronic systems. Irrespective of the wide variety of preventative measures, spurious signals are received and carried by data channels to one extent or another.
Shielding, coaxial cables, twisted pairs and differential input amplifiers, to name a few preventative measures, have been used by designers and to one degree or another helped eliminate spurious signals. Other times, unwanted electronic pickups are removed by filtering; but here again, filtering is not always effective particularly in the case where there are significant frequency components in the neighborhood of the desired authentic data being transmitted through the system. Spurious signal problems are recurring and bothersome if the transmission lines are long.
An error checking circuit for a digital system was disclosed by Kevin C. Stodola in U.S. Pat. No. 4,342,112. The circuit detected failures on a dual redundant bus structure was capable of detecting single point failures within the error checking circuit itself. The circuit provides for what it calls a two rail logic in which signals are generated in both true and complement form on two rails of output flip-flops. The generated signals present on the two rails of a signal pair are intended always to be complementary. An error is indicated if the two rails of any signal pair are not complementary. Any error at any signal pair within the two rail logic error circuit will be transmitted to the following logic in the circuit such that the error may be detected at the final output of the circuit. Thus, any error presented to the checking circuit, or occurring within the circuit, will be indicated at the final output of the circuit. As a further refinement the output logic states on the two rails are changed from time to time so that the various logic gates within the checking circuit are frequently used so that a fault or defect occurring within the circuit itself is readily detectable. Circuit and bus failure are identified and appropriate action can be taken.
Irrespective of the meritorious advances for error reduction, there is a continuing need in the state-of-the-art for an apparatus and method for detecting spurious signals picked up and transmitted between at least one sensor and its data storage station that removes spurious signals from the valid data prior to its being recorded.